The invention relates to the field of beam splitters and in particular to broadband beam splitters with matched group delay dispersion for all input and output ports.
Beam splitters are essential devices in the entire field of optics. They are used to combine or split optical beams at the same wavelength or with different wavelength. Specifically, broadband beam splitters are important in ultrafast optics to combine and split ultrashort optical pulse streams without spectral or spatial distortions. The conventional techniques for very broadband beam splitter are either based on thin metal layer or dielectric multi-layer thin-film structures.
Metallic beam splitters consist of a thin metal layer such as gold, aluminum or silver that is deposited on a glass or similar material substrate. Although metallic beam splitters have a broad operating wavelength range and are widely used for ultrafast optics applications, they show considerable loss and strong wavelength dependence in reflection and transmission owing to the wavelength dependent penetration depth into the metal. Conventional dielectric beam splitters based on quarter-wave Bragg stacks cannot support such broad spectra. For high quality pulse synthesis or splitting, it is highly desirable to design a broadband beam splitter based on multi-layer dielectric thin-film coatings deposited on a stable substrate.